This invention relates to a device for measuring the number of revolutions of the shaft of a permanent magnet electric motor.
In numerous applications in the automotive field electric motors are used to provide proportional control systems for the movement of components of the vehicle, such as the engine throttle, the regulating systems, storage and automatic positioning of the seats and/or of the rear view mirrors, etc.
The measurement of the total rotation or displacement obtained is frequently very important and revolution or displacement sensors are generally used.
Where the actuator consists of a permanent magnet reduction motor, the problem of measuring the number of revolutions is normally solved by adopting one of the following solutions:
recording the number of revolutions of the motor shaft by means of sensors of the optical type, or Hall effect type, or more rarely by means of electromagnetic sensors; knowing the motor reduction ratio the angular position or the displacement of the reduction motor can be calculated; PA1 direct measurement of the angle of rotation (if no greater than 3600) of the shaft of the reduction motor, or of the axial displacement by means of sensors of the potentiometric type, or linear Hall effect sensors.
It has been found that the use of sensors is not entirely satisfactory from the point of view of space occupied, cost and the need to provide electrical connections to a control and data processing station normally present in the vehicle.